The present invention relates to a high frequency or radio frequency inductively coupled plasma mass spectrometry apparatus (hereinafter, referred to as "ICP-MS") for carrying out analysis of a trace element contained in a sample solution.
ICP-MS apparatus typical of the prior art, as shown in FIG. 2, is comprised of a plasma torch 1 for producing a plasma 2, a sampling orifice 3 which has a small opening diameter, a skimmer orifice 4 having a small opening diameter for passing an ion beam 5, a lens 6, a deflector 7, a junction member 8c, a mass filter 9, a detector 10, a power supply 11 for powering an optical system, an I/0 interface 12, a computer 13, and a display device 14.
A sample solution (not shown) is fed to the plasma torch 1 together with a carrier gas such as argon to form the plasma 2, which is injected through the sampling orifice 3. A sampling interface is formed by the sampling orifice 3, the skimmer orifice 4 and a vacuum region between orifices 3 and 4. A vacuum is created in the latter region by a suitable vacuum device (not shown).
Plasma torch 1 emits plasma 2 toward sampling orifice 3 and this plasma travels along a path having an introduction axis which extends through, and is centered in, orifices 3 and 4. The plasma 2 passes through the sampling interface to form the ion beam 5.
The optical system is composed of lens 6 having an optical axis aligned with the above-mentioned introduction axis, deflector 7 and junction member 8c and functions to introduce the ion beam 5 efficiently to mass filter 9 while blocking light emitted from plasma 2. Namely, deflector 7 deflects ion beam 5 from the introduction axis of plasma torch 1, the sampling interface and the lens 6 to a laterally offset exit axis defined by a passage in junction 8c and mass filter 9 so as to block light, which travels along linear paths, from reaching mass filter 9. At the same time, lens 6 operates to focus ion beam 5 onto an inlet of mass filter 9, which inlet is defined by the passage in junction member 8c.
The ion beam 5 which enters mass filter 9 contains various ion species and a given ion species having a particular mass specified by computer 13 can reach an outlet of the mass filter, while other ion species will be diverted in mass filter 9. The ion species passing through mass filter 9 is detected by detector 10 and the detected ions are counted. The counting result is fed through I/0 interface 12 to computer 13.
Computer 13 operates to identify a particular trace element within the sample solution and to calculate the concentration thereof according to the counting result from detector 10 and the mass information fed to mass filter 9. The identification and calculation results are indicated in display device 14.
The mass filter is normally composed of a quadrupole mass spectrometer, and the detector is composed of a channeltron. The optical system, mass filter 9 and detector 10 are disposed within a high vacuum space evacuated by a vacuum pump (not shown). Adjustment of the lens 6 and deflector 7 is manually carried out by the operator, together with regulating of power supply 11 for the optical system while monitoring the output level of detector 10.
In the conventional apparatus, as described above, adjustment of the optical system is effected manually based solely on the output signal from detector 10. This has given rise to various problems. For example, adjustment is extremely time-consuming and complicated, especially when the operator is not fully familiar with the structure and features of the optical system. Moreover, the results of the quantity analysis may not be reliable, especially in the lower critical range of the detector, when the solution analysis is undertaken with incomplete adjustments.